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Oceanography Seminar
Monday, 15 September 2003
11:00 am – 12:00 noon
Center Green 1 Board Room
(3080 Center Green Drive, room 3416)
Abstract:
Nearly
all state of the art coupled climate models suffer from the
cold-tongue problem, i.e., they simulate an eastern Pacific
cold-tongue that significantly
colder than observed. Most models simply fail to
capture the boreal spring warming when the observed SSTs are at
their annual maximum. This chronic
problem which clearly affects the models'
ability to predict seasonal to interannual variability is typically
blamed on the deficient stratus deck simulation. However, even
forced OGCMs of present day simulate
a cold bias in the eastern equatorial
Pacific when no corrective fluxes or feedbacks to observed SSTs are
enforced, no-matter which winds are employed to force the models.
Subsurface observations show that during boreal spring months, the
water column restratifies in the
cold tongue region due to weak winds and the
annual peak in incident radiation. Ocean modelers assign the blame
to vertical mixing
parameterizations. However, it is shown with the help of
satellite ocean-color derived attenuation depths and with a coupled
biogeochemical model, that the unique conditions during the boreal
spring favor a subsurface Chl-a maximum which converts light to
heat below the mixed layer, leading
to a natural restratification of the water
column. This biological feedback is crucial for simulating the
annual cycle of SSTs in the eastern Pacific cold tongue. Coupled
ocean-atmosphere-ecosystem model simulations show that this
feedback also affects the amplitude
and frequency of the interannual variability
in the tropical Pacific. The consequences for ENSO prediction and
tropical climate variability are discussed.
For more information, contact: Lisa
Butler
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